Data transfer devices which form a communication network, such as a layer 2 switch, IP router or layer 3 switch, transfer a received Ethernet (Ethernet: proprietary product name) frame, IP packet or MPLS packet transmitted by the MPLS method, to an output circuit corresponding to the address data of this packet. To reduce power consumption in the data transfer device accompanying the increase in traffic, various power consumption reduction methods are being examined.
As a way of reducing power consumption during content addressable memory access, there is a method wherein look-up conditions are first arranged in a desired registration order in a content addressable memory, and rearranged in order of increasing (or decreasing) value (e.g., Patent document 1). At this time, the value of the look-up condition situated at the boundary of each physical bank in the content addressable memory is stored in a register. In this example, a data look-up device of low power consumption is provided by limiting the physical banks to be looked up by the value of the look-up key generated from the inputted data, when looking up the look-up condition using the content addressable memory by comparing with the value of this register, and activating only the limited physical banks.
In addition, there is a method wherein, to reduce power consumption in a content addressable memory for routing of received IP packets, a physical bank to be activated is decided by a hash function (e.g., Non-patent document 1).
[Patent document 1] JP-A No. 185792/2004
[Non-patent document 1] [Hidell et al], “Router Architectures” Tutorial at Networking 2004, http://www.imit.kth.se/˜mahidell/pubs/networking04_tutorial_final.pdf, pp. 41